Black soldier fly larvae (BSFL), the larval stage of Hermetia illucens, are garnering increasing attention for their voracious appetite and ability to convert organic waste into valuable biomass. Their diet is a key factor in their effectiveness as waste managers, sustainable feed producers, and even potential food sources for humans. This article delves into the intricate details of what black soldier fly larvae eat, how their diet impacts their nutritional composition, and the broader implications of their feeding habits.
What Black Soldier Fly Larvae Consume
The question of what black soldier fly larvae eat has a multifaceted answer, contingent on their environment and purpose. In their natural habitat, wild black soldier fly larvae function as detritivores and coprivores, feeding on decaying organic material, particularly plant matter, and feces. However, their adaptability extends to a wide array of organic waste, including manure, carrion, compost, food scraps, and virtually any other type of decomposing organic matter.
The Larval Diet: A Feast of Organic Waste
Black soldier fly larvae are remarkably versatile eaters, consuming a wide range of organic materials:
- Food Waste: Fruits, vegetables, and other kitchen scraps, including spoiled or leftover food, are readily consumed by BSFL.
- Agricultural Waste: Crop residues, plant material, spent grains from breweries, and other byproducts of farming serve as a food source.
- Manure: Animal manure, including that from poultry, cattle, and pigs, is efficiently processed by BSFL, making them useful in agricultural systems for managing livestock waste.
- Other Organic Materials: Rotting meat, fish, and dairy products can also be part of their diet.
What Adults Eat
Adult black soldier flies have greatly reduced sponging mouthparts and can only consume liquids such as flower nectar or do not eat at all. Instead, they rely on the energy reserves accumulated during their larval stage. They may sip on water or nectar but do not contribute to waste recycling. During their short 5-8 day lifespan, they primarily live on the fat that they stored as larvae.
Nutritional Composition and Diet
Like most feeders, what black soldier fly larvae are raised on significantly affects their nutritional composition. Moistened chicken feed is a common baseline used in research papers, but high-quality black soldier fly larvae tend to be raised on a specifically-formulated grain and grass diet, likely with added calcium.
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Nutritional Value of BSFL
Black soldier fly larvae (BSFL) are rich in nutrients such as fat, protein and high-quality amino acids and minerals, making them a good source of protein.
In animal feed, there are currently two types of BSFL: defatted and full fat, with the primary difference being in fat and saturated fatty acid content. The average crude protein content of BSFL was 414.7 g/kg, ranging from 216 g/kg to 655 g/kg, which was lower than a conventional soybean meal (CSBM) (494.4 g/kg) and fish meal (675.3 g/kg). In full-fat BSFL, the fat content ranged from 294 g/kg to 515.3 g/kg, with an average of 353.2 g/kg; these were both higher than CSBM (14 g/kg) and fish meal (103.6 g/kg). The average fat level after defatting (69.2 g/kg) was also higher than CSBM. BSFL contained ash at an average of 82.4 g/kg, ranging from 27 g/kg to 132 g/kg, higher than CSBM (71.9 g/kg) and lower than fish meal (171.5 g/kg). The average level of crude fiber was 95.4 g/kg, ranging from 41 g/kg to 213 g/kg, which was lower than CSBM (74.3 g/kg), but higher than fish meal (2.6 g/kg). The average content of chitin was 61.7 g/kg, ranging from 38.7 to 72.1 g/kg.
Amino Acid Profile
Both defatted and full-fat BSFL have a rich amino acid profile and are thus considered a more sustainable protein source than CSBM or fish meal. The most abundant essential amino acids were leucine (average 44.6 g/kg, from 27.8 g/kg to 78.3 g/kg), lysine (average 38.8 g/kg, from 23.0 g/kg to 68.2 g/kg) and valine (average 40.1 g/kg, ranging from 28.2 g/kg to 67.9 g/kg). These three amino acid contents are higher than those of soybean meal, and even the valine content is higher than that of fish meal. The least abundant essential amino acids are methionine and tryptophan, which are comparable to soybean meal and are much lower than fish meal. The content of histidine ranged from 9.8 g/kg to 48 g/kg, and the content of isoleucine ranged from 17.7 g/kg to 48 g/kg, which was slightly higher than soybean meal and fish meal. The content of phenylalanine ranged from 16.4 g/kg to 77.6 g/kg, and the content of threonine ranged from 16.2 g/kg to 45 g/kg, which are basically the same as soybean meal and fish meal.
Fatty Acid Composition
The most abundant saturated fatty acids (SFA) are lauric acid (C12:0), which ranges from 75 to 575. An amount of 6 g/kg, myristic acid (C14:0), which ranges from 23 to 98.7 g/kg, palmitic acid (C16:0), which ranges from 10.3 to 192.0 g/kg, and stearic acid (C18:0), which ranges from 9.8 to 69.0 g/kg. The highest content of monounsaturated fatty acids is oleic acid (c9C18:1), which ranges from 79.7 to 266.0 g/kg, palmitoleic acid (C16:1), which ranges from 10.3 to 192.0 g/kg, linoleic acid (C18:2n6), which ranges from 38.0 to 314.0 g/kg, and linolenic acid (C18:3n3), which ranges from 9.8 to 36.0 g/kg. SFA content ranges from 362.0 to 782.9 g/kg, MUFA ranges from 85.5 to 287.0 g/kg, n-6 PUFA ranges from 80.0 to 314.0 g/kg and n-3 PUFA ranges from 9.8 to 36.0 g/kg.
Mineral Content
BSFL are rich in minerals; calcium (Ca) is the most abundant and ranges from 1.2 g/kg to 35.7 g/kg. Copper (Cu) ranges from 0.1 g/kg to 15.0 g/kg. Iron (Fe) ranges from 0.1 g/kg to 191.0 g/kg. Magnesium (Mg) ranges from 1.0 g/kg to 3.5 g/kg. Manganese (Mn) ranges from 0.2 g/kg to 166.0 g/kg. Phosphorus (P) ranges from 1.0 g/kg to 10.3 g/kg. Potassium (K) ranges from 1.7 g/kg to 15.4 g/kg. Sodium (Na) ranges from 0.7 g/kg to 15.6 g/kg. Zinc (Zn) ranges from 0.7 g/kg to 103.0 g/kg.
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Factors Affecting Nutritional Composition
The nutritional composition of BSFL is influenced by several factors:
- Growth Stage: The crude fat content of larvae increases rapidly between the 4th and 14th days, while crude protein shows a continuous downward trend.
- Nutritional Structure: The fat and ash content varies greatly depending on whether BSFL are fed vegetable waste, chicken feed, or kitchen waste.
- Processing Method: Different killing methods (such as blanching, drying, freezing, high hydrostatic pressure grinding, and asphyxiation) affect pH, ash, fat content, and oxidative capacity.
- Environmental Factors: Temperature, humidity, sunlight, moisture content, and pH levels also play a role in nutrient composition.
Practical Considerations for Raising BSFL
When you buy black soldier fly larvae, they are typically stored in a small plastic tub of soil, sawdust, or bran. The black soldier fly larvae that you receive when you purchase them as feeders for your pet actually don’t need to be fed! Just like they don’t need food, dormant black soldier fly larvae don’t need water, either. However, if you wish to raise the larvae into flies, they will need a water source.
If you want to provide food because you want to raise the larvae into flies, the good news is that you don’t actually have to feed them. If you buy large black soldier fly larvae, they will readily pupate without additional food, given the right environmental conditions. If you want to feed them, though, they will eat just about anything you give them.
Ideal Conditions for BSFL Growth
Temperatures between 26 and 40 °C and relative humidity between 40-70% are the ideal living conditions for BSFL. Sunlight also affects the nutrient composition of BSFL, with black soldier flies developing best in the wavelength range between 450 and 700 nm. When the water content in the feed matrix is 60-80%, the survival rate and growth rate of BSFL are the highest. The growth of black soldier flies is better under alkaline conditions than under acidic conditions, and a suitable pH value is between 6-9.
The Broader Implications of BSFL Diets
The black soldier fly’s feeding habits have significant environmental and economic benefits:
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- Waste Reduction: Their larvae can reduce organic waste volume by up to 70%.
- Sustainability: They convert low-value waste into high-value protein and compost (frass).
- Circular Economy: The larvae themselves can be harvested as a sustainable feed for livestock and aquaculture.
BSFL in Animal Feed
Although BSFL cannot completely replace soybean meal in poultry diets, supplementation of less than 20% has no negative impact on chicken growth performance, biochemical indicators and meat quality. In pig studies, although BSFL supplementation did not have any negative effect on growth performance and meat quality, the feed conversion ratio (FCR) was reduced.
Challenges and Future Directions
The use of BSFL in animal feed presents some challenges in terms of cost, availability and legal and consumer acceptance. Moreover, it has not been found that BSFL are used in ruminants, and the next phase of research could therefore study them.
Personal Experiences with BSFL
I raise worms to make my garden grow better. Well, earlier this year I started getting a ton of black soldier fly larvae eating the extra worm food that I put down. For months I’ve been taking the larvae out and putting them in a bin for the birds. Which has been great for the birds and I have counted 18 different species of birds at the house.
I couldn’t resist and I clicked on a few of the links. Within an hour I was out in the garden collecting the larvae for dinner. And let me tell you, I’m excited about the possibility of actually raising black soldier flies because they are a great source of fat and protein. Those are the two main nutrients my vegetable garden doesn’t give me. Here are a few black soldier fly larvae in the garden. They eat just about any plant or animal. Even though this is the first time I’ve harvested black soldier flies to eat for myself, I’ve been collecting them for the birds for 8 months.
First I sift the soil to get the big stuff out of it. The container below this tub has 1/8 hardware cloth, and most of the black soldier fly larvae can squeeze right through that if I give them 15 or 20 minutes. After I separated out the flies, I put them in a strainer and rinsed them. Since they live in my garden soil, they had a lot of dirt on them. I’ve learned that you can raise black soldier fly larvae in sawdust though. Once I rinsed them off, I dumped them in a white tub while I got things ready in the kitchen. I discovered that they poop a lot.
Now for the cooking. Then I added the worms. It was interesting. They smelled absolutely delicious, kinda nutty. But when they got too hot or cooked too much, I’m not sure which, they started popping like popcorn! That is amazingly good! Overall, I’d say this was a huge success and I really enjoyed eating black soldier flies.